JP7679366B2 - Manufacturing carbon fibers with high mechanical properties - Google Patents

Description

The present invention relates to a method for producing carbon fibers.

Carbon fiber (CF or graphite fiber) is a carbonaceous material, typically a thread or filament with a diameter of about 5-10 μm, composed primarily of at least 50% carbon atoms by weight. Carbon fiber is widely used in aerospace, civil engineering, military, motor sports and sporting goods due to its many advantages, including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature resistance and low thermal expansion.

Carbon fiber is typically produced using two main methods, either from the use of polyacrylonitrile (PAN) or from pitch. Pitch is the product of the distillation of carbon-based materials such as plants, crude oil, and coal. Pitch is isotropic, but can be made anisotropic by heat treatment. However, the most important material in carbon fiber production is mesophase pitch due to the ability to melt spin anisotropic mesophase pitch without filament breakage. Mesophase pitch forms thermotropic crystals that allow the pitch to organize and form straight chains without the use of tension.

Mesophase pitch is made by polymerizing isotropic pitch to high molecular weights. The advantage in the production of pitch-based carbon fibers over PAN carbon fibers is that pitch carbon fibers do not require constant tension on the fiber at all processing stages.

Pitch-based carbon fibers are found to be more sheet-like in crystal structure, in contrast to PAN-based carbon fibers, which are more granular. There are six main steps in the production of carbon fibers from pitch: 1) melt spinning, 2) oxidation, 3) carbonization, 4) graphitization, 5) surface treatment, and 6) sizing.

Melt spinning is a method of forming fibers by rapid cooling of the melt. The rapid cooling rate allows mesophase pitch to become highly oriented. Mesophase pitch can be melt spun, but due to its flow properties, the process can be difficult to carry out reliably. The viscosity of mesophase pitch is more sensitive to temperature than other melt-spun materials. Therefore, temperature and heat transfer rates must be carefully controlled during the production of pitch-based fibers.

Oxidation is used to crosslink the molecules to the point where the fiber will not melt or fuse. This is usually carried out in air at about 200°C to about 400°C for several hours. This step is crucial to producing fibers that are stable at the high temperatures of carbonization and graphitization. Without crosslinking, the fiber would be damaged during these process steps.

Carbonization is accomplished by heating the fibers to high temperatures, typically about 1000°C to about 2000°C, in an inert, oxygen-free atmosphere. This step removes most of the impurities (e.g., hydrogen, oxygen, nitrogen) from the fibers, leaving primarily crystalline carbon in mostly hexagonal rings.

Graphitization is a process in which fibers are treated at high temperatures to improve the alignment and orientation of the crystalline regions along the primary fiber axis. By aligning, stacking, and orienting the crystalline regions along the primary fiber axis, the overall strength and stiffness of the carbon fiber is increased. To obtain carbon fibers with a higher modulus and higher carbon content, graphitization is carried out at higher temperatures, up to 3000°C.

Surface treatments can be applied to improve adhesion of carbon fibers to a binding matrix for producing composite materials. Finally, carbon fiber sizing involves coating surface-treated carbon fibers with polymers to prevent breakage of individual filaments, improve handling of very fine carbon filaments, and provide compatibility with molding processes.

The high strength of carbon fiber can be attributed to the six main processes mentioned above. The high level of crystalline regions allows the fiber to withstand large stresses. These crystalline regions are formed by the melt spinning process, and the crystals are rigid regions that do not easily deform when external stress is applied.

Asphaltenes are molecular substances found in carbonaceous materials such as bitumen or crude oil, or coal, along with resins, aromatic hydrocarbons, and saturates. Asphaltenes have complex molecular structures containing aromatic polycyclic structures surrounded by aliphatic chains and heteroatoms, and they are usually insoluble in light n-alkanes (such as n-pentane, _nC5 or n-heptane, _nC7 ), but soluble in aromatic solvents such as toluene. Their molecular weights are usually found in the range of 400u to 1500u, but the average and maximum values are difficult to determine due to the aggregation of the molecules in solution. Asphaltenes consist mainly of carbon, hydrogen, nitrogen, oxygen, and sulfur, with traces of vanadium, nickel, and iron. The C:H ratio is about 1:1.2, depending on the asphaltene source.

Asphaltenes are the major component of pitch-based precursors for carbon fiber. For example, asphaltenes make up more than 80% by weight of the total Ashland 260 petroleum pitch, a trade name for a high-grade pitch precursor for carbon fiber.

Pure asphaltene is a glass-like solid and can be easily ground into powder at ambient temperature. No attempt has been made to produce carbon fibers from pure solid asphaltene. It is known to produce carbon fibers from asphaltene obtained from heavy oil upgrading, where a liquid phase asphaltene stream at room temperature containing about 60% to about 70% asphaltene is introduced through a spinneret to obtain carbon-based filaments. If solid asphaltene is available, a step of dissolving the solid phase asphaltene stream in a solvent to obtain an asphaltene solution is necessary before introducing the asphaltene-containing liquid phase through a spinneret to obtain carbon-based filaments. In the latter case, the solid phase asphaltene stream contains about 60% to about 90% asphaltene, where the total weight of the solid phase asphaltene stream is taken as 100% by weight, before dissolving in the solvent.

It is also known to use electrospinning to produce both solid and hollow micrometer-sized fibers from asphaltenes. However, no further processing to achieve high mechanical properties has been carried out. Such processing is an essential step for carbon fibers to reach the mechanical properties required to produce composite materials. Moreover, the fibers after electrospinning appear short, bent, hollow and branched. These defects do not meet the basic requirements of carbon fibers for structural applications.

This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should it be construed, that any of the preceding information constitutes prior art against the present invention.

The present invention relates to a method for producing carbon-based fibers by melt spinning of solid asphaltenes, which may preferably be asphaltenes eliminated by solvent deasphalting of feedstock bitumen or crude oil. The feedstock may be pyrolytic or non-pyrolytic. The melt-spun carbon-based fibers are then treated to achieve desired mechanical properties.
One embodiment of the present invention will be described below, but the present invention is not limited thereto.
[Invention 1]
1. A method for producing carbon fibers, comprising the steps of:
(a) melting asphaltene solids in a closed vessel;
(b) spinning the molten asphaltene to produce green fibers;
(c) stabilizing the green fiber in a liquid or gas environment; and
(d) carbonizing the stabilized green fiber
The method includes:
[Invention 2]
2. The method of claim 1, wherein the green fibers are stabilized in air or steam.
[Invention 3]
3. The method of claim 1 or 2, wherein the asphaltene solids are melted in step (a) at about 150° C. to about 550° C. in an environment such as nitrogen, hydrogen, or steam, or a mixture thereof.
[Invention 4]
4. The method according to any one of claims 1 to 3, wherein step (a) extends to about 6 hours.
[Invention 5]
The method according to claim 4, wherein step (a) extends from 0.5 hours to 2 hours.
[Invention 6]
6. The method according to any one of claims 1 to 5, wherein in step (a), the sealed container is pressurized to a level of from 0 to about 1000 kPa during heating.
[Invention 7]
7. The method of any one of claims 1 to 6, wherein the spinning step comprises pulling the molten asphaltene through a spinneret to produce the green fiber, and winding the green fiber onto a rotating spool.
[Invention 8]
The method according to claim 7, wherein the temperature of the asphaltene during spinning is controlled to about 150°C to about 350°C.
[Invention 9]
9. The method according to claim 7 or 8, wherein the pressure in the closed vessel during spinning is controlled to about 100 kPa to about 1000 kPa, preferentially about 200 kPa to about 700 kPa.
[Invention 10]
10. The method according to claim 7, 8 or 9, wherein the speed of the rotating spool is controlled to achieve a fibre pulling speed of between 50 and 1000 metres per minute, preferentially between 100 and 300 metres per minute.
[Invention 11]
11. The method according to any one of claims 7 to 10, wherein the diameter of the spinneret is selected to a size ranging from about 50 to about 300 μm, preferentially from about 100 to about 200 μm.
[Invention 12]
12. The method according to any one of claims 1 to 11, wherein the green fibres are produced with a diameter in the size range of about 1 to about 15 μm, preferentially about 7 to about 10 μm.
[Invention 13]
13. The method according to any one of claims 1 to 12, wherein the green fibres are stabilized by immersion in an aqueous solution which coats the green fibres and prevents clumping between adjacent green fibres.
[Invention 14]
14. The method of claim 13, wherein the aqueous solution comprises hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, derivatives thereof, and/or mixtures thereof.
[Invention 15]
15. The method of claim 13 or 14, wherein the aqueous solution may be concentrated or diluted, the dilution may range from 1% to 100% by weight of the concentrated solution.
[Invention 16]
16. The method according to claim 13, 14 or 15, wherein the immersion time is between 1 second and 100 minutes, preferentially between 5 seconds and 50 minutes.
[Invention 17]
17. The method according to any one of the preceding claims, wherein said stabilization step comprises at least one heat treatment step at a temperature between 100°C and 400°C in an air or steam environment.
[Invention 18]
18. The method according to claim 17, wherein said stabilization step comprises at least two temperature steps, such as 2 to 5 steps, preferentially 2 to 3 steps.
[Invention 19]
19. The method according to claim 17 or 18, wherein each temperature step lasts from 0.5 h to 24 h.
[Invention 20]
20. The method according to any one of claims 1 to 19, wherein the carbonization step comprises at least one heat treatment step at a temperature of about 400°C to about 1600°C in an inert environment such as nitrogen gas.
[Invention 21]
21. The method of claim 20, wherein the at least one stage heat treatment comprises at least a low temperature stage and a high temperature stage.
[Invention 22]
22. The method of claim 20 or 21, wherein the low temperature stage is carried out at about 400° C. to about 600° C. for a period of about 0.5 to about 3 hours.
[Invention 23]
23. The method according to claim 21 or 22, further comprising an intermediate temperature stage carried out at a temperature of about 700° C. to about 900° C. for a period of about 0.5 to about 10 hours, preferentially about 1 to about 3 hours.
[Invention 24]
24. The method of any one of claims 21 to 23, wherein the high temperature stage is carried out at a temperature of about 1300°C to about 1600°C for a period of 0.5 to 10 hours.
[Invention 25]
21. The method of claim 20, wherein the heat treatment step includes an intermediate temperature step without a low or high temperature step.
[Invention 26]
21. The method of claim 20, wherein the heat treatment step comprises a high temperature step without a low temperature or intermediate temperature step.
[Invention 27]
27. The method according to any one of claims 1 to 26, wherein the diameter of the carbon fibers after final treatment is controlled in the range of about 5 to about 10 μm.
[Invention 28]
28. The method of any one of claims 1 to 27, wherein the solid asphaltenes are processed to reduce or change the content of sulfur, oxygen, metal species, specific molecular species or groups prior to melt spinning.
[Invention 29]
29. The method according to any one of claims 1 to 28, wherein the solid asphaltene can be added or heat treated with other chemicals to change the temperature of melt spinning, to change the chemical nature of the asphaltene, to increase the mesophase content, and/or to change the viscosity of the molten asphaltene.
[Invention 30]
30. The method according to any one of claims 1 to 29, comprising the further step of graphitizing the carbonized fibers.
[Invention 31]
30. A carbon fiber obtainable by the method according to any one of claims 1 to 29.

In one aspect, the present invention provides a method for producing carbon fibers, comprising the steps of:
(a) melting the asphaltene solids in a closed vessel by heating and pressurizing the vessel using an inert gas;
b) introducing the molten asphaltenes into a spinneret to obtain green fibers;
c) surface pre-treating the green fiber by stabilizing it with a liquid or gas to avoid possible fiber fusion during subsequent heat treatment; and d) heat treating the surface treated green fiber.
In some embodiments, green fibers can be produced with desired fiber diameters by controlling the spinneret pull speed and diameter.

Embodiments of the present invention generally relate to a method for producing carbon fibers directly from asphaltene solids without the need to generate a liquid stream containing asphaltene and introduce the liquid stream into a spinneret to obtain carbon-based fibers. In particular, no solvent is required to dissolve the asphaltene.

A more detailed description of the invention, briefly described above, continues with reference to the following drawings of specific embodiments of the invention. The drawings depict only typical embodiments of the invention and therefore should not be considered as limiting its scope. The drawings are not necessarily to scale and in some cases proportions may be exaggerated to more clearly show certain features.

FIG. 1 shows the relationship between spool take-up speed of raw asphaltene (referred to as green fiber) and filament diameter established using a melt spinning apparatus to produce filaments of asphaltene.

FIG. 1 is a heat flow-temperature diagram of raw asphaltene with and without heat treatment at 260° C. for 1 hour in nitrogen.

FIG. 1 shows the effect of the holding time of molten asphaltene before introduction into the spinneret to obtain green fibers on the tensile strength of carbon fibers after stabilization at 350° C. in air for 2 hours and carbonization at 800° C. in nitrogen for 2 hours.

FTIR-ART (Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection Accessory) spectra showing attenuated infrared light as interferogram signal after treating the raw fiber with the following processes/steps: Top spectrum: asphaltene-derived raw fiber after immersion in 17% nitric acid for 10 minutes, middle spectrum: asphaltene-derived raw fiber after immersion in 17% nitric acid for 10 minutes and thorough washing with deionized water, bottom spectrum: untreated asphaltene-derived raw fiber.

Figure 1 shows the tensile strength of carbon fibers after stabilization and carbonization treatments carried out at 350°C for 2 hours in air and at 800°C for 2 hours in nitrogen, respectively. The green fibers were pretreated at 150°C in air for various times before carrying out the stabilization and carbonization treatments shown above.

Figure 1 shows the tensile modulus of carbon fibers after stabilization and carbonization treatments carried out at 350°C for 2 hours in air and at 800°C for 2 hours in nitrogen, respectively. The green fibers were pretreated at 150°C in air for various times before carrying out the stabilization and carbonization treatments shown above.

FIG. 1 shows the tensile strength of carbon fibers after stabilization in air at 350° C. for 2 hours, and first stage carbonization in nitrogen at various temperatures for 2 hours, and second stage carbonization in nitrogen at 800° C. for 2 hours.

FIG. 1 shows the tensile strength of carbon fibers after stabilization in air at 350° C. for 2 hours and carbonization in nitrogen at various temperatures for 2 hours.

FIG. 1 shows the tensile strength of carbon fibers after stabilization in air at 350° C. for 2 hours and carbonization in nitrogen at various temperatures for 2 hours.

FIG. 1 is a graph of the tensile modulus of carbon fibers after stabilization treatment at 350° C. in air for 2 hours and carbonization treatment at various temperatures in nitrogen for 2 hours.

1 is an image of a fracture cross section of carbon fiber after carbonization at 800° C. for 8 hours.

Figure 2 shows the melt spinning temperature of the same asphaltene feedstock pretreated in a nitrogen environment for 2 hours at different temperatures up to 350°C before melt spinning into green fiber. This treatment increased the melt spinning temperature to produce green fiber. Note that the feedstock used in this study is different from the feedstock used in the study shown in Figure 2.

The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to be limited to the invention in the form disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The embodiments have been selected and described to best explain the principles and practical applications of the invention and to enable those skilled in the art to understand the invention in its various embodiments with various modifications suited to the particular applications contemplated. To the extent that the following description is directed to a particular embodiment or a particular use of the invention, it is intended to be illustrative only and not limiting of the claimed invention.

As used herein, "carbon fiber" refers to any yarn or filament material containing at least 50% (by mass) elemental carbon with a yarn or filament diameter of less than 0.1 mm, which can be controlled to achieve either higher force or stress to break. The term "fiber" may be spelled interchangeably with "fiber."

Asphaltene solids for the production of carbon fibers shall refer to solid precipitates obtained by adding a solvent such as n-alkanes (like n-pentane, _nC5 or n-heptane, _nC7 ) to bitumen or crude oil. This process is commonly known as solvent deasphalting by those skilled in the art, is well known and does not require further explanation. This deasphalting process can be applied directly to bitumen and crude oil or after some thermal conversion step or cracking, resulting in asphaltene solids that are insoluble in the selected solvent. Asphaltenes have the above mentioned properties and composition and are also well known to those skilled in the art.

The present invention relates to a method for producing carbon fibers using solid asphaltene as a carbon precursor. Table 1 provides typical compositions of asphaltene solids from different sources. The method embodiments disclosed herein can be applied to asphaltene from any source, as long as the asphaltene is in a solid phase. Preferably, the asphaltene is substantially free of solid particles having a melting point greater than about 100° C. or a size greater than about 1 μm. In some preferred embodiments, asphaltene precursors containing relatively little sulfur, oxygen, any metal species, and fine non-melted particles may be preferred for producing carbon fibers with improved mechanical properties.

Carbon fibers produced by the methods disclosed herein can achieve high strength. The strength of carbon fibers is very sensitive to the diameter of the carbon fiber. The diameter of carbon fibers produced by the methods disclosed herein can be larger than that of commercially available carbon fibers of the prior art, which are typically less than 10 μm, with most in the range of 5-7 μm. In contrast, the diameter of carbon fibers produced herein can range from 10-16 μm. These fibers can be tested to demonstrate the effect of heat treatment on the mechanical properties of carbon fibers produced using pure solid asphaltene as the carbon precursor.

In some embodiments, solid asphaltene is added to a closed chamber and then melted under pressure in an inert atmosphere. For example, in one embodiment, the asphaltene may be melted at about 190° C. and pressurized to about 0 to about 1000 kPa, preferably about 200 to about 600 kPa, more preferably about 400 kPa using nitrogen gas. A spinneret of appropriate size may be placed at the bottom of the chamber, for example a 150 μm diameter spinneret may be used. The asphaltene filaments may be drawn from the spinneret and wound onto a rotating spool, such as a 20 cm diameter spool. The rotational speed of the spool is preferably adjustable. The diameter of the asphaltene filaments or green fibers is inversely proportional to the rotational speed of the spool, as shown in FIG. 1.

The appropriate temperature and pressure for melt spinning can be modified by the temperature and time the asphaltenes are held in the melt chamber before being spun into carbon fibers. In one embodiment, the bulk asphaltenes may be held in a closed chamber in nitrogen at about 260°C for 1 hour before melt spinning. Such extended heat treatment increases the temperature point at which the asphaltenes begin to soften from about 175°C to about 245°C, as can be seen in Figure 2.

In one embodiment, the bulk asphaltene was held at 350°C for 1, 2 and 3 hours, respectively, prior to melt spinning, along with a 0 hour control. The resulting asphaltene fibers were subjected to the same post-melt spinning steps (stabilization and carbonization), which were carried out at 350°C in air for 2 hours and at 800°C in nitrogen for 2 hours, respectively. It is seen that the tensile strength of the carbon fibers after all treatments is highest when the bulk asphaltene treatment is maintained at 350°C for 1 hour prior to melt spinning.

Figure 12 shows the melt spinning temperature of the same asphaltene feedstock pretreated in a nitrogen environment for 2 hours at different temperatures up to 350°C before melt spinning into green fiber. This treatment increased the melt spinning temperature to produce green fiber. Note that the feedstock used in this study is different from the feedstock used in the study shown in Figure 2.

The melt-spun green fibers must be stabilized, for example by surface treating the green fibers with a liquid or gas, prior to carbonization and/or graphitization. If the stabilization is carried out at a temperature higher than the temperature at which the asphaltenes are melt-spun into green fibers, fusion of green fibers that are in physical contact with each other may occur during heating from ambient temperature to the stabilization temperature.

In some embodiments, the melt spun green fibers may be immersed in a liquid that coats or interacts with the green fiber surface to prevent fusion between adjacent fibers. Suitable liquids include dilute or concentrated mineral acids, such as hydrochloric acid, nitric acid, or sulfuric acid; organic acids, such as phytic acid; or solutions of inorganic salts, such as potassium salts, such as potassium nitrate, potassium chloride; or derivatives of any of the foregoing; and/or mixtures thereof. In one preferred embodiment, the green fibers may be immersed in a nitric acid solution (17%) for 10 minutes to prevent fusion of physically contacted green fibers during heating to temperatures above those used for melt spinning. Immersion in the nitric acid solution may attach chemical species to the surface of the green fibers, preventing the green fibers from fusing with adjacent fibers. If the nitric acid immersed green fibers are rinsed with water, the coated chemical species are removed and fusion of physically attached green fibers may occur again during heating to temperatures above those used for melt spinning.

In some embodiments, the green fibers may be stabilized or further stabilized in a graded temperature regime in air. In one embodiment, the green fibers may be first immersed in 17% nitric acid for 10 seconds and stabilized in air at 150°C for various times up to 24 hours, preferably at least about 16 hours, followed by a second stabilization treatment at 350°C for 2 hours. The stabilized fibers are then carbonized at 800°C for 2 hours. Exemplary results for various treatment times at 150°C are shown in Figure 5.

The stabilized green fibers may be carbonized, for example, at a temperature in the range of about 400°C to about 1600°C, preferably in an inert or nitrogen environment. The carbonization step may be performed in one stage or in multiple stages. For example, a three-stage carbonization process may be appropriate, having an initial low-temperature stage at a temperature in the range of 400°C to 600°C, an intermediate temperature stage in the range of 600°C to about 1200°C (preferably 800°C to 1000°C), and a final high-temperature stage in the range of about 1200°C to about 1600°C (preferably about 1500°C). Each stage may last from a few minutes to a few hours, for example, each stage may last from about 1 hour to about 2 hours.

In some embodiments, the results of which are shown in FIG. 7, the raw fibers were carbonized in low and intermediate temperature stages before tensile testing. The first carbonization stage was performed at different temperatures ranging from 400°C to 600°C for 2 hours, and the second carbonization stage was performed at 800°C for 2 hours. The best tensile strength was achieved when the first carbonization stage was performed at 500°C for 2 hours. In other embodiments, the results of which are shown in FIG. 8, a low temperature carbonization stage was performed at 500°C for 2 hours, followed by an intermediate temperature carbonization stage at temperatures ranging from 800°C to 1000°C for 2 hours. The lowest tensile strength was observed when the intermediate carbonization stage was performed at 900°C for 2 hours, and the highest tensile strength was observed when the intermediate carbonization stage was performed at 800°C.

In some embodiments, the results of which are shown in Figures 9 and 10, high temperature carbonization was performed at 1500°C for various times ranging from 2 hours to 8 hours, with or without a prior intermediate temperature step. The best tensile strength was achieved when the carbonization at 1500°C lasted for 2 hours without a prior intermediate temperature step. The tensile strength decreased when the carbonization time at 1500°C was increased beyond 2 hours. When an intermediate temperature carbonization at 800°C was performed prior to the high temperature treatment at 1500°C, the tensile strength decreased compared to the tensile strength obtained when high temperature carbonization was performed alone.

The observed decrease in strength when asphaltene-derived carbon fibers are carbonized near 900° C. is believed to be due to the formation of aggregates of metal-containing compounds within the fibers. As seen in FIG. 11, after intermediate temperature carbonization at 800° C. for 8 hours, the destructed carbon fibers show several aggregates of metal-containing phases with the chemical composition shown in Table 2.
Table 2 lists the chemical composition of the central aggregate shown in FIG.

Treatment of raw fibers can cause changes in the chemical properties of the carbon fibers. In one embodiment, the carbon, nitrogen, hydrogen, and sulfur compositions were analyzed after various treatments, and the results are shown in Table 3. In general, the carbon content in the carbon fibers increased with increasing treatment temperature and treatment time, while the nitrogen, hydrogen, and sulfur contents decreased with increasing treatment temperature and treatment time.

Table 3 lists the chemical composition of asphaltenes and asphaltene-derived carbon fibers after various stages of treatment at different temperatures for different times.

Optionally, the carbon fibers produced may be graphitized. Graphitization is a process in which the fibers are treated at high temperatures to improve the alignment and orientation of the crystalline regions along the primary fiber axis. By aligning, stacking, and orienting the crystalline regions along the primary fiber axis, the overall strength and stiffness of the carbon fibers is increased. To obtain carbon fibers with a higher modulus and higher carbon content, graphitization is carried out at higher temperatures, up to about 3000°C.

In view of the above discussion, certain more detailed embodiments of the present invention are presented below. However, these detailed recited embodiments should not be construed as having any limiting effect on any different claims that incorporate different or more general teachings set forth herein, nor should the "specific" embodiments be construed as being limited in any way other than in the inherent meaning of the language literally used therein.

Aspect 1: A method for producing carbon fibers, comprising:
(a) melting asphaltene solids in a closed vessel;
(b) spinning the molten asphaltene to produce green fibers;
(c) stabilizing the green fiber in a liquid or gas environment;
(d) carbonizing the stabilized green fibers; and (e) optionally, graphitizing the carbonized fibers.

Aspect 2: The method of claim 1, wherein the green fiber is stabilized in air or steam.

Aspect 3: The method of aspect 1 or 2, wherein the asphaltene solids are melted in step (a) at about 150°C to about 550°C in an environment such as nitrogen, hydrogen, or steam, or a mixture thereof.

Aspect 4: The method of any one of aspects 1 to 3, wherein step (a) is extended to about 6 hours.

Aspect 5: The method of aspect 4, wherein step (a) is extended to 0.5 hours to 2 hours.

Aspect 6: The method of any one of aspects 1 to 5, wherein in step (a), the sealed container is pressurized to a level of 0 to about 1000 kPa during heating.

Aspect 7: The method of any one of aspects 1 to 6, wherein the spinning step includes pulling the molten asphaltene through a spinneret to produce the green fiber, and winding the green fiber onto a rotating spool.

Aspect 8: The method of aspect 7, wherein the temperature of the asphaltene during spinning is controlled to about 150°C to about 350°C.

Aspect 9: The method according to aspect 7 or 8, in which the pressure in the sealed vessel during spinning is controlled to about 100 kPa to about 1000 kPa, preferentially about 200 kPa to about 700 kPa.

Aspect 10: The method of aspect 7, 8 or 9, wherein the speed of the rotating spool is controlled to achieve a fiber pull speed of 50 to 1000 meters per minute, preferentially 100 to 300 meters per minute.

Aspect 11: The method according to any one of aspects 7 to 10, wherein the diameter of the spinneret is selected to a size in the range of about 50 to about 300 μm, preferentially about 100 to about 200 μm.

Aspect 12: The method of any one of aspects 1 to 11, wherein the raw fibers are produced to a size in the range of about 1 to about 15 μm in diameter, preferentially about 7 to about 10 μm.

Aspect 13: The method of any one of aspects 1 to 12, wherein the green fibers are stabilized by immersion in an aqueous solution that coats the green fibers and prevents aggregation between adjacent green fibers.

Aspect 14: The method of aspect 13, wherein the aqueous solution comprises hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, derivatives thereof, and/or mixtures thereof.

Aspect 15: The method of aspect 13 or 14, wherein the aqueous solution may be concentrated or diluted, and the dilution may range from 1% to 100% by weight of the concentrated solution.

Aspect 16: The method according to aspect 13, 14 or 15, wherein the immersion time is from 1 second to 100 minutes, preferentially from 5 seconds to 50 minutes.

Aspect 17: The method of any one of aspects 1 to 16, wherein the stabilization step includes at least one heat treatment step at a temperature between 100°C and 400°C in an air or steam environment.

Aspect 18: The method according to aspect 17, wherein the stabilization step includes at least two temperature steps, such as 2 to 5 steps, preferentially 2 to 3 steps.

Aspect 19: The method of aspect 17 or 18, wherein each temperature step lasts from about 0.5 hours to about 24 hours.

Aspect 20: The method according to any one of aspects 1 to 19, wherein the carbonization step includes at least one heat treatment step at a temperature of about 400°C to about 1600°C in an inert environment, such as nitrogen gas.

Aspect 21: The method of aspect 20, wherein the at least one heat treatment step includes at least a low-temperature step and a high-temperature step.

Aspect 22: The method of aspect 20 or 21, wherein the low temperature stage is carried out at about 400°C to about 600°C for a period of about 0.5 to about 3 hours.

Aspect 23: The method of aspect 21 or 22, further comprising an intermediate temperature stage carried out at a temperature of about 700°C to about 900°C for a period of about 0.5 to about 10 hours, preferentially about 1 to about 3 hours.

Aspect 24: The method of any one of aspects 21 to 23, wherein the high temperature stage is carried out at a temperature of about 1300°C to about 1600°C for a period of 0.5 to 10 hours.

Aspect 25: The method of aspect 20, wherein the heat treatment step includes an intermediate temperature step without a low or high temperature step.

Aspect 26: The method of aspect 20, wherein the heat treatment step includes a high temperature step without a low temperature or intermediate temperature step.

Aspect 27: The method according to any one of aspects 1 to 26, wherein the diameter of the carbon fibers after final processing is controlled to a range of about 5 to about 10 μm.

Aspect 28: The method of any one of aspects 1 to 27, wherein the solid asphaltenes are processed to reduce or change the content of sulfur, oxygen, metal species, specific molecular species or groups prior to melt spinning.

Aspect 29: The method of any one of aspects 1 to 28, wherein the solid asphaltene can be added or heat treated with other chemicals to change the melt spinning temperature, change the chemistry of the asphaltene, increase the mesophase content, and/or change the viscosity of the molten asphaltene.

Aspect 30: The method of any one of aspects 1 to 29, modified or supplemented by any step, feature or element described herein.

Aspect 31: Carbon fibers obtained by the method according to any one of aspects 1 to 30.

DEFINITIONS AND INTERPRETATION References herein to "one embodiment,""anembodiment," and the like indicate that the described embodiment may include a particular aspect, feature, structure, or characteristic, but not all embodiments necessarily include that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referenced elsewhere in this specification. Furthermore, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one of ordinary skill in the art to combine, affect, or connect such aspect, feature, structure, or characteristic with other embodiments, whether or not such connection or combination is explicitly described. In other words, any element or feature can be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility between the two, or unless specifically excluded.

It is further noted that the claims may be drafted to exclude any optional element. Accordingly, this statement is intended to serve as a predicate for the use of exclusive terms such as "solely" and "only" in connection with the recitation of claim elements or the use of a "negative" limitation. The terms "preferably," "preferred," "preferable," "optionally," "may," and similar terms are used to indicate that the referred item, condition, or step is an optional (but not required) feature of the invention.

The singular forms "a," "an," and "the" include plural references unless the context clearly indicates otherwise. The term "and/or" means any one of the items, any combination of the items, or all of the items with which this term is associated.

As will be understood by those skilled in the art, for any and all purposes, particularly with respect to providing a written description, all ranges recited herein also encompass any and all possible subranges and combinations of subranges thereof, as well as the individual values, particularly integer values, that make up the range. A recited range (e.g., weight percent or carbon group) includes each specific value, integer, decimal, or identity within the range. Any recited range can be readily recognized as fully descriptive and allowing for division of the same range into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range described herein can be readily divided into a lower third, a middle third, an upper third, and so forth.

Also, as will be understood by one of ordinary skill in the art, all language such as "up to,""atleast,""greaterthan,""lessthan,""morethan,""greater than or equal to," and the like, are inclusive of the recited numbers and such terms refer to ranges that can be subsequently divided into subranges as described above. Similarly, all ratios recited herein also include all subratios that fall within the broader ratio range.

References
The following documents and any publications mentioned therein are indicative of the level of skill of those skilled in the art, and are hereby incorporated by reference in their entirety, where permitted:

Claims (23)

1. A method for producing carbon fibers, comprising the steps of:
(a) melting in a closed vessel the asphaltene solids obtained from the solvent deasphalting process;
(b) spinning the molten asphaltene to produce green fibers;
(c) stabilizing the green fiber in a liquid or gas environment; and (d) carbonizing the stabilized green fiber. The method of claim 1 , wherein the green fibers are stabilized in air or water vapor . 3. The method of claim 1 or 2, wherein the asphaltene solids are melted in step (a) at 150° C. to 550° C. in a gaseous environment comprising nitrogen, hydrogen, or water vapor , or a mixture thereof. The method according to any one of claims 1 to 3, wherein the melting in step (a) is carried out for 0.5 hours to 2 hours. 5. The method of any one of claims 1 to 4, wherein in step (a), the sealed container is pressurized to a level of 200 to 1000 kPa during heating. The method of any one of claims 1 to 5, wherein the spinning step includes pulling the molten asphaltene through a spinneret to produce the green fiber, and winding the green fiber onto a rotating spool. The method according to claim 6, wherein the temperature of the asphaltene during spinning is controlled to 150° C. to 350° C. , and/or the pressure of the closed vessel during spinning is controlled to 200 kPa to 700 kPa . The method of claim 6 or 7, wherein the speed of the rotating spool is controlled to achieve a fiber pulling speed of 50 to 1000 meters per minute. The method according to any one of claims 6 to 8, wherein the diameter of the spinneret is selected to a size in the range of 50 to 300 μm and the diameter of the green fibres produced is in the range of 1 to 15 μm . The method of any one of claims 1 to 9, wherein the biofibers are stabilized by immersion in an aqueous solution that coats the biofibers and prevents aggregation between adjacent biofibers, the aqueous solution comprising hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, derivatives thereof, and/or mixtures thereof. The method according to claim 10, wherein the immersion time is from 5 seconds to 50 minutes. The method according to any one of claims 1 to 11 , wherein the stabilisation step comprises or further comprises at least one heat treatment step at a temperature between 100°C and 400°C in an air or water vapour environment. The method of claim 12 , wherein the stabilization step comprises at least two temperature steps. 14. The method according to claim 12 or 13 , wherein each temperature step lasts from 0.5 hours to 24 hours. 11. The method of claim 10 , wherein the aqueous solution comprises a 17% nitric acid solution. The method according to any one of the preceding claims, wherein the carbonization step comprises at least one heat treatment step at a temperature between 400°C and 1600°C in an inert environment. 17. The method of claim 16 , wherein the at least one stage heat treatment comprises at least one low temperature stage and at least one high temperature stage. The method of claim 17 further comprising an intermediate temperature stage carried out at a temperature of 700° C. to 900° C. for a period of 0.5 to 10 hours. A method according to claim 17 or 18 , wherein said at least one high temperature stage is carried out at a temperature of from 1300° C. to 1600° C. for a period of from 0.5 to 10 hours. The method according to any one of claims 1 to 19 , wherein the carbon fibres have a diameter in the range of 5 to 10 µm. 21. The method of any one of claims 1 to 20 , wherein a solid asphaltene precursor is used that has been processed to reduce or change the content of sulfur, oxygen, or metal species prior to melt spinning. 22. The method of any one of claims 1 to 21, wherein the solid asphaltene can be added or heat treated with other chemicals to change the melt spinning temperature, change the chemistry of the asphaltene, increase the mesophase content, and/or change the viscosity of the molten asphaltene. The method of any one of claims 1 to 22 , comprising the further step of graphitizing the carbonized fibers.

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